If you build an aicraft to MTOW of 600kg the structure will be too heavy for UL category. Excuse my scepticism here. Any illustration or example? It seems unlikely to me that, for just one example, the FK-9 would be built on a different frame to qualify as an LSA, the cost of development would be heavy. At most, some extra stiffeners/gussets might be added, or sturdier landing gear. Also, the...